WASHINGTON — Democratic Sen. Max Baucus, the powerful Senate Finance chairman who steered President Barack Obama's health care overhaul into law but broke with his party on gun control, said Tuesday he will not run for re-election.

"I don't want to die here with my boots on. There is life beyond Congress," the 71-year-old Baucus said in a telephone interview with The Associated Press.

Baucus, who arrived in Washington as a member of the 1974 Watergate class in the House and has been a fixture in the Senate since 1979, said the decision was hard.

"It was probably the most difficult decision in my life," Baucus said.

He faced a tough re-election bid next year, with opposition to the health care law in his state taking a toll on his approval ratings.

A Democrat with an independent streak, Baucus supported the Bush tax cuts of 2001 and Obama's signature 2010 health care law. He broke with his party this year to oppose both the Senate Democratic budget blueprint and a hotly fought effort to beef up background checks for gun purchases.

Baucus, who helped write Obama's health care law, stunned administration officials last week when he told the president's health care chief that he thought the law was headed for a "train wreck" because of bumbling implementation.

Baucus was the first top Democrat to publicly voice fears about the rollout of the new health care law, designed to bring coverage to some 30 million uninsured people through a mix of government programs and tax credits for private insurance. Polls show that Americans remain confused by the complex law, and even many uninsured people are skeptical they will be helped by benefits that start next year.

Baucus' retirement opens up an opportunity for Republicans to claim a Senate seat in a state where GOP presidential nominee Mitt Romney easily defeated Obama by 12 percentage points last year. But Democrats have proved resilient in Montana, with Sen. Jon Tester winning re-election last year. The election of Steve Bullock last year is the third term in a row in which Democrats have held the governorship.

Former two-term Democratic Gov. Brian Schweitzer indicated an interest in the race in an interview with The Associated Press.

"The opportunity to try and get the country moving again like we did in Montana, that's appealing," Schweitzer said. "I'm a fixer."

Republican campaign officials, who last week seized upon Baucus' comments on the health care law, sought to tar other Democratic Senate candidates in a statement Tuesday responding to Baucus' decision.

"Just days after calling Obamacare a 'train wreck,' its architect Max Baucus waved the white flag rather than face voters," said Rob Collins, executive director of the National Republican Senatorial Committee. "Obamacare has gone from being an 'abstract' discussion to a real life pain for workers and families, which has Democratic candidates like Bruce Braley, Mark Pryor, Mark Begich and Kay Hagan backpedaling. ... The 2014 electoral map is in free-fall for Democrats, who were already facing a daunting challenge."

Possible Republican candidates are former Gov. Marc Racicot; Denny Rehberg, the former congressman who lost a bitter race last year to Tester; Rick Hill, another former congressman who lost to Bullock; and Steve Daines, the current Montana congressman.

The only Republicans who have declared their intention to run is state Sen. Champ Edmunds of Missoula and former state Sen. and gubernatorial candidate Corey Stapleton.

Democrats in the Senate will be defending 21 seats next year to Republicans 14, with several Democrats running for re-election in GOP-leaning states that Romney won handily. Among the Democrats facing tough challenges next year are Sens. Mark Begich of Alaska, Mary Landrieu of Louisiana and Mark Pryor of Arkansas.

Democrats also have more retirements than the GOP. Five Democrats in addition to Baucus have announced they will not seek another term: Jay Rockefeller of West Virginia, Tom Harkin of Iowa, Frank Lautenberg of New Jersey, Carl Levin of Michigan and Tim Johnson of South Dakota.

Among Republicans, Saxby Chambliss of Georgia and Mike Johanns of Nebraska have decided to retire.

Sen. Michael Bennet, D-Colo., who heads the Democratic Senatorial Campaign Committee, touted last year's re-election of Tester and said, "We will continue to invest all the resources necessary to hold this seat."

Despite his standing as a top Democrat in Capitol Hill, Baucus sometimes bucked the party line in recognition of Montana being a fundamentally conservative state with voters who want someone willing to base votes on more than party lines.

"I don't focus on labels," he has said. "For me, Montana comes first and partisan labels are a distant second."

He was an architect of the President George W. Bush's prescription drug plan in 2003, one of the few Democrats to back a GOP-led effort to provide prescription drug coverage under Medicare. The law is now widely popular with Republicans and Democrats.

Baucus is from a wealthy Helena ranching family. He practiced law in Montana in the early 1970s until he was elected to the state House in 1973. He first won election to the U.S. House as part of the huge 1974 Watergate class and easily moved up to the Senate in 1978. He has had only one close race since, when he defeated then Lt. Gov. Denny Rehberg with less than 50 percent of the vote in 1996.

Baucus became an advocate for the residents of the Montana town of Libby after news reports in 1999 linked asbestos contamination from a vermiculite mine there to deaths and illnesses. He helped deliver money to those who fell sick and became a vocal critic of both the W.R. Grace Co., and the Environmental Protection Agency for not doing enough to clean up the town.

He also worked to protect the land bordering Glacier National Park by advocating energy companies to retire their leases in the North Fork watershed of Montana's Flathead River.

Baucus voted in favor of invading Iraq, but said later that his vote was a mistake based on faulty intelligence delivered to Congress. After his nephew was killed while deployed in Iraq, Baucus said in later years that the troops should come home as soon as possible.

Baucus ran afoul of his constituents during President Bill Clinton's administration when he supported a handgun-control law and a ban on the sale of some assault-style weapons. Gun ownership is widespread in Montana, and Baucus later supported allowing those laws to expire in 2004.

Baucus came under criticism in February 2009 when he recommended Melodee Hanes for Montana's U.S. attorney post when he was dating her. Hanes withdrew her name from consideration in March and was hired in June as a top official in the Justice Department.

She and Baucus married in June 2011 at the historic Montana ranch north of Helena run by his family.

Baucus attended Stanford University, where he earned a bachelor's degree in 1964 and a law degree in 1967. He worked as an attorney with the Civil Aeronautics Board from 1967 to 1968, and with the Securities and Exchange Commission from 1968 to 1971. He practiced law in Montana from 1971 to 1974.